The contamination of water by halogenated hydrocarbons is a serious environmental problem. Currently, methods to treat such water and gas include air stripping and absorption on activated carbon. Both methods result not in the destruction of the chlorinated compounds but only in their transfer to another media. Investigations of biological methods for treating halegonated hydrocarbon contamination have identified three biological systems which can metabolize these components.
Anaerobic organisms are able to carry out reductive dehalogenation of tetrachloroethylene and trichloroethene, (Vogel, et al. "Biotransformation of Tetrachloroethylene to trichloroethylene, dichloroethylene, Vinyl Chloride and Carbon Dioxide Under Methanogenic Conditions", Appl. Environ. Microbiol. 49, 5 (May 1985) pp. 1080-1083). However, this process results in the accumulation of vinyl chloride which is decomposed slowly to ethylene under anaerobic conditions (Freedman and Gossett, "Biological Reductive Dechlorination of Tetrachloroethylene and Trichloroethylene to Ethylene under Methanogenic Conditions", Appl. Environ. Microbiol, 55, 9 (Sept. 1989), pp. 2144-2151). Two aerobic systems have been described in which halogenated hydrocarbons are co-metabolized in the presence of another carbon source. Nelson et al. "Aerobic Metabolism of Trichloroethylene by Bacterial Isolate", Appl. Environ. Microbiol, 52, 2 (August 1986) pp. 383-384 have described a bacterium which metabolizes chlorinated hydrocarbons during growth on phenol, toluene or other aromatic compounds which are degraded by the meta-cleavage pathway. The chlorinated compounds are apparently first attacked by a dioxygenase and then finally metabolized to inorganic chloride and carbon dioxide. This process has limited application to environmental situtations due to the toxicity of the toluene or phenol food source.
The third biological system employs methanotrophs. These bacteria are aerobes which depend on methane as their sole source of carbon. Fogel et al., "Biodegradation of Chlorinated Ethenes by a Methane-Utilizing Mixed Culture", Appl. Environ. Microbiol., 51, 4 (Apr. 1986), pp. 720-724, showed that these organisms metabolize trichloroethylene in the presence of methane. Further studies confirmed that these organisms could decompose a wide range of halogenated hydrocarbons, including dichloroethylene, ethylene dibromide 1,1,1-trichloroethylene, vinyl chloride, methylene chloride (Fogel et al., "Bioodegradation of Chlorinated Aliphatic Compounds by Methane-Oxidizing Bacteria: Mechanisms and Products", final report to the National Science Foundation, Award No. ISI-8560700, 1986).
No other biological systems for decomposing chlorinated hydrocarbons have been described. U.S. Pat. No. 4,749,491 to Lawes et al. claims an aerobic process which does not require a primary source of carbon in addition to the chlorinated compound. However, exhaustive investigations reported in the scientific literature have not detected organisms capable of this metabolic feat (Vogel et al., "Transformation of Halogenated Aliphatic Compounds", Environ. Sci. Technol. 21, 8 (August 1987), pp. 772-736, 1987).
The present invention employs methanotrophs to degrade halogenated hydrocarbons in a rotating biological contactor (RBC).